diff --git a/Cargo.lock b/Cargo.lock
index 001e664..29cab6d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4,30 +4,30 @@ version = 3
 
 [[package]]
 name = "aho-corasick"
-version = "0.7.20"
+version = "1.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cc936419f96fa211c1b9166887b38e5e40b19958e5b895be7c1f93adec7071ac"
+checksum = "8e60d3430d3a69478ad0993f19238d2df97c507009a52b3c10addcd7f6bcb916"
 dependencies = [
  "memchr",
 ]
 
 [[package]]
 name = "anyhow"
-version = "1.0.70"
+version = "1.0.83"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7de8ce5e0f9f8d88245311066a578d72b7af3e7088f32783804676302df237e4"
+checksum = "25bdb32cbbdce2b519a9cd7df3a678443100e265d5e25ca763b7572a5104f5f3"
 
 [[package]]
 name = "autocfg"
-version = "1.1.0"
+version = "1.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
+checksum = "0c4b4d0bd25bd0b74681c0ad21497610ce1b7c91b1022cd21c80c6fbdd9476b0"
 
 [[package]]
 name = "base64"
-version = "0.21.0"
+version = "0.21.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a4a4ddaa51a5bc52a6948f74c06d20aaaddb71924eab79b8c97a8c556e942d6a"
+checksum = "9d297deb1925b89f2ccc13d7635fa0714f12c87adce1c75356b39ca9b7178567"
 
 [[package]]
 name = "bindgen"
@@ -35,7 +35,7 @@ version = "0.69.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a00dc851838a2120612785d195287475a3ac45514741da670b735818822129a0"
 dependencies = [
- "bitflags 2.4.0",
+ "bitflags",
  "cexpr",
  "clang-sys",
  "itertools",
@@ -66,24 +66,17 @@ checksum = "349f9b6a179ed607305526ca489b34ad0a41aed5f7980fa90eb03160b69598fb"
 
 [[package]]
 name = "bitflags"
-version = "1.3.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
-
-[[package]]
-name = "bitflags"
-version = "2.4.0"
+version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b4682ae6287fcf752ecaabbfcc7b6f9b72aa33933dc23a554d853aea8eea8635"
+checksum = "cf4b9d6a944f767f8e5e0db018570623c85f3d925ac718db4e06d0187adb21c1"
 
 [[package]]
 name = "bstr"
-version = "1.4.0"
+version = "1.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c3d4260bcc2e8fc9df1eac4919a720effeb63a3f0952f5bf4944adfa18897f09"
+checksum = "05efc5cfd9110c8416e471df0e96702d58690178e206e61b7173706673c93706"
 dependencies = [
  "memchr",
- "once_cell",
  "regex-automata",
  "serde",
 ]
@@ -105,9 +98,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "clang-sys"
-version = "1.6.0"
+version = "1.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "77ed9a53e5d4d9c573ae844bfac6872b159cb1d1585a83b29e7a64b7eef7332a"
+checksum = "67523a3b4be3ce1989d607a828d036249522dd9c1c8de7f4dd2dae43a37369d1"
 dependencies = [
  "glob",
  "libc",
@@ -116,15 +109,15 @@ dependencies = [
 
 [[package]]
 name = "either"
-version = "1.10.0"
+version = "1.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "11157ac094ffbdde99aa67b23417ebdd801842852b500e395a45a9c0aac03e4a"
+checksum = "a47c1c47d2f5964e29c61246e81db715514cd532db6b5116a25ea3c03d6780a2"
 
 [[package]]
 name = "fancy-regex"
-version = "0.11.0"
+version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b95f7c0680e4142284cf8b22c14a476e87d61b004a3a0861872b32ef7ead40a2"
+checksum = "7493d4c459da9f84325ad297371a6b2b8a162800873a22e3b6b6512e61d18c05"
 dependencies = [
  "bit-set",
  "regex",
@@ -159,25 +152,25 @@ checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
 
 [[package]]
 name = "libc"
-version = "0.2.140"
+version = "0.2.154"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "99227334921fae1a979cf0bfdfcc6b3e5ce376ef57e16fb6fb3ea2ed6095f80c"
+checksum = "ae743338b92ff9146ce83992f766a31066a91a8c84a45e0e9f21e7cf6de6d346"
 
 [[package]]
 name = "libloading"
-version = "0.7.4"
+version = "0.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b67380fd3b2fbe7527a606e18729d21c6f3951633d0500574c4dc22d2d638b9f"
+checksum = "0c2a198fb6b0eada2a8df47933734e6d35d350665a33a3593d7164fa52c75c19"
 dependencies = [
  "cfg-if",
- "winapi",
+ "windows-targets",
 ]
 
 [[package]]
 name = "lock_api"
-version = "0.4.9"
+version = "0.4.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "435011366fe56583b16cf956f9df0095b405b82d76425bc8981c0e22e60ec4df"
+checksum = "07af8b9cdd281b7915f413fa73f29ebd5d55d0d3f0155584dade1ff18cea1b17"
 dependencies = [
  "autocfg",
  "scopeguard",
@@ -185,9 +178,9 @@ dependencies = [
 
 [[package]]
 name = "magnus"
-version = "0.6.1"
+version = "0.6.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0516897a45f8ce8270a8910bcb94cd83538b19b6ae3a0c281a765df170b64695"
+checksum = "b1597ef40aa8c36be098249e82c9a20cf7199278ac1c1a1a995eeead6a184479"
 dependencies = [
  "magnus-macros",
  "rb-sys",
@@ -208,9 +201,9 @@ dependencies = [
 
 [[package]]
 name = "memchr"
-version = "2.5.0"
+version = "2.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
+checksum = "6c8640c5d730cb13ebd907d8d04b52f55ac9a2eec55b440c8892f40d56c76c1d"
 
 [[package]]
 name = "minimal-lexical"
@@ -228,17 +221,11 @@ dependencies = [
  "minimal-lexical",
 ]
 
-[[package]]
-name = "once_cell"
-version = "1.17.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b7e5500299e16ebb147ae15a00a942af264cf3688f47923b8fc2cd5858f23ad3"
-
 [[package]]
 name = "parking_lot"
-version = "0.12.1"
+version = "0.12.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3742b2c103b9f06bc9fff0a37ff4912935851bee6d36f3c02bcc755bcfec228f"
+checksum = "7e4af0ca4f6caed20e900d564c242b8e5d4903fdacf31d3daf527b66fe6f42fb"
 dependencies = [
  "lock_api",
  "parking_lot_core",
@@ -246,49 +233,49 @@ dependencies = [
 
 [[package]]
 name = "parking_lot_core"
-version = "0.9.7"
+version = "0.9.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9069cbb9f99e3a5083476ccb29ceb1de18b9118cafa53e90c9551235de2b9521"
+checksum = "1e401f977ab385c9e4e3ab30627d6f26d00e2c73eef317493c4ec6d468726cf8"
 dependencies = [
  "cfg-if",
  "libc",
  "redox_syscall",
  "smallvec",
- "windows-sys",
+ "windows-targets",
 ]
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.66"
+version = "1.0.82"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "18fb31db3f9bddb2ea821cde30a9f70117e3f119938b5ee630b7403aa6e2ead9"
+checksum = "8ad3d49ab951a01fbaafe34f2ec74122942fe18a3f9814c3268f1bb72042131b"
 dependencies = [
  "unicode-ident",
 ]
 
 [[package]]
 name = "quote"
-version = "1.0.33"
+version = "1.0.36"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5267fca4496028628a95160fc423a33e8b2e6af8a5302579e322e4b520293cae"
+checksum = "0fa76aaf39101c457836aec0ce2316dbdc3ab723cdda1c6bd4e6ad4208acaca7"
 dependencies = [
  "proc-macro2",
 ]
 
 [[package]]
 name = "rb-sys"
-version = "0.9.87"
+version = "0.9.97"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "225103e3d69bbfe8831f9fd0d2461335f3a9dd06aa6e88bcb6d6970383494d06"
+checksum = "47d30bcad206b51f2f66121190ca678dce1fdf3a2eae0ac5d838d1818b19bdf5"
 dependencies = [
  "rb-sys-build",
 ]
 
 [[package]]
 name = "rb-sys-build"
-version = "0.9.87"
+version = "0.9.97"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bacce8095a5167d5ede618bbd9353e9d9e2f32ddaf54be911106f0ee6baacf09"
+checksum = "3cbd92f281615f3c2dcb9dcb0f0576624752afbf9a7f99173b37c4b55b62dd8a"
 dependencies = [
  "bindgen",
  "lazy_static",
@@ -307,35 +294,41 @@ checksum = "a35802679f07360454b418a5d1735c89716bde01d35b1560fc953c1415a0b3bb"
 
 [[package]]
 name = "redox_syscall"
-version = "0.2.16"
+version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fb5a58c1855b4b6819d59012155603f0b22ad30cad752600aadfcb695265519a"
+checksum = "469052894dcb553421e483e4209ee581a45100d31b4018de03e5a7ad86374a7e"
 dependencies = [
- "bitflags 1.3.2",
+ "bitflags",
 ]
 
 [[package]]
 name = "regex"
-version = "1.7.1"
+version = "1.10.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "48aaa5748ba571fb95cd2c85c09f629215d3a6ece942baa100950af03a34f733"
+checksum = "c117dbdfde9c8308975b6a18d71f3f385c89461f7b3fb054288ecf2a2058ba4c"
 dependencies = [
  "aho-corasick",
  "memchr",
+ "regex-automata",
  "regex-syntax",
 ]
 
 [[package]]
 name = "regex-automata"
-version = "0.1.10"
+version = "0.4.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6c230d73fb8d8c1b9c0b3135c5142a8acee3a0558fb8db5cf1cb65f8d7862132"
+checksum = "86b83b8b9847f9bf95ef68afb0b8e6cdb80f498442f5179a29fad448fcc1eaea"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
 
 [[package]]
 name = "regex-syntax"
-version = "0.6.28"
+version = "0.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "456c603be3e8d448b072f410900c09faf164fbce2d480456f50eea6e25f9c848"
+checksum = "adad44e29e4c806119491a7f06f03de4d1af22c3a680dd47f1e6e179439d1f56"
 
 [[package]]
 name = "rustc-hash"
@@ -345,9 +338,9 @@ checksum = "08d43f7aa6b08d49f382cde6a7982047c3426db949b1424bc4b7ec9ae12c6ce2"
 
 [[package]]
 name = "scopeguard"
-version = "1.1.0"
+version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
+checksum = "94143f37725109f92c262ed2cf5e59bce7498c01bcc1502d7b9afe439a4e9f49"
 
 [[package]]
 name = "seq-macro"
@@ -357,9 +350,23 @@ checksum = "a3f0bf26fd526d2a95683cd0f87bf103b8539e2ca1ef48ce002d67aad59aa0b4"
 
 [[package]]
 name = "serde"
-version = "1.0.157"
+version = "1.0.202"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "707de5fcf5df2b5788fca98dd7eab490bc2fd9b7ef1404defc462833b83f25ca"
+checksum = "226b61a0d411b2ba5ff6d7f73a476ac4f8bb900373459cd00fab8512828ba395"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_derive"
+version = "1.0.202"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6048858004bcff69094cd972ed40a32500f153bd3be9f716b2eed2e8217c4838"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
 
 [[package]]
 name = "shell-words"
@@ -369,21 +376,21 @@ checksum = "24188a676b6ae68c3b2cb3a01be17fbf7240ce009799bb56d5b1409051e78fde"
 
 [[package]]
 name = "shlex"
-version = "1.1.0"
+version = "1.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "43b2853a4d09f215c24cc5489c992ce46052d359b5109343cbafbf26bc62f8a3"
+checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"
 
 [[package]]
 name = "smallvec"
-version = "1.10.0"
+version = "1.13.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a507befe795404456341dfab10cef66ead4c041f62b8b11bbb92bffe5d0953e0"
+checksum = "3c5e1a9a646d36c3599cd173a41282daf47c44583ad367b8e6837255952e5c67"
 
 [[package]]
 name = "syn"
-version = "2.0.31"
+version = "2.0.63"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "718fa2415bcb8d8bd775917a1bf12a7931b6dfa890753378538118181e0cb398"
+checksum = "bf5be731623ca1a1fb7d8be6f261a3be6d3e2337b8a1f97be944d020c8fcb704"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -392,8 +399,9 @@ dependencies = [
 
 [[package]]
 name = "tiktoken-rs"
-version = "0.3.2"
-source = "git+https://github.com/IAPark/tiktoken-rs.git#5231fbf4a91d9221a713522e755445d0dde341fa"
+version = "0.5.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c314e7ce51440f9e8f5a497394682a57b7c323d0f4d0a6b1b13c429056e0e234"
 dependencies = [
  "anyhow",
  "base64",
@@ -415,50 +423,20 @@ dependencies = [
 
 [[package]]
 name = "unicode-ident"
-version = "1.0.8"
+version = "1.0.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e5464a87b239f13a63a501f2701565754bae92d243d4bb7eb12f6d57d2269bf4"
-
-[[package]]
-name = "winapi"
-version = "0.3.9"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
-dependencies = [
- "winapi-i686-pc-windows-gnu",
- "winapi-x86_64-pc-windows-gnu",
-]
-
-[[package]]
-name = "winapi-i686-pc-windows-gnu"
-version = "0.4.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
-
-[[package]]
-name = "winapi-x86_64-pc-windows-gnu"
-version = "0.4.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
-
-[[package]]
-name = "windows-sys"
-version = "0.45.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "75283be5efb2831d37ea142365f009c02ec203cd29a3ebecbc093d52315b66d0"
-dependencies = [
- "windows-targets",
-]
+checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b"
 
 [[package]]
 name = "windows-targets"
-version = "0.42.2"
+version = "0.52.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8e5180c00cd44c9b1c88adb3693291f1cd93605ded80c250a75d472756b4d071"
+checksum = "6f0713a46559409d202e70e28227288446bf7841d3211583a4b53e3f6d96e7eb"
 dependencies = [
  "windows_aarch64_gnullvm",
  "windows_aarch64_msvc",
  "windows_i686_gnu",
+ "windows_i686_gnullvm",
  "windows_i686_msvc",
  "windows_x86_64_gnu",
  "windows_x86_64_gnullvm",
@@ -467,42 +445,48 @@ dependencies = [
 
 [[package]]
 name = "windows_aarch64_gnullvm"
-version = "0.42.2"
+version = "0.52.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "597a5118570b68bc08d8d59125332c54f1ba9d9adeedeef5b99b02ba2b0698f8"
+checksum = "7088eed71e8b8dda258ecc8bac5fb1153c5cffaf2578fc8ff5d61e23578d3263"
 
 [[package]]
 name = "windows_aarch64_msvc"
-version = "0.42.2"
+version = "0.52.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e08e8864a60f06ef0d0ff4ba04124db8b0fb3be5776a5cd47641e942e58c4d43"
+checksum = "9985fd1504e250c615ca5f281c3f7a6da76213ebd5ccc9561496568a2752afb6"
 
 [[package]]
 name = "windows_i686_gnu"
-version = "0.42.2"
+version = "0.52.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "88ba073cf16d5372720ec942a8ccbf61626074c6d4dd2e745299726ce8b89670"
+
+[[package]]
+name = "windows_i686_gnullvm"
+version = "0.52.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c61d927d8da41da96a81f029489353e68739737d3beca43145c8afec9a31a84f"
+checksum = "87f4261229030a858f36b459e748ae97545d6f1ec60e5e0d6a3d32e0dc232ee9"
 
 [[package]]
 name = "windows_i686_msvc"
-version = "0.42.2"
+version = "0.52.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "44d840b6ec649f480a41c8d80f9c65108b92d89345dd94027bfe06ac444d1060"
+checksum = "db3c2bf3d13d5b658be73463284eaf12830ac9a26a90c717b7f771dfe97487bf"
 
 [[package]]
 name = "windows_x86_64_gnu"
-version = "0.42.2"
+version = "0.52.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8de912b8b8feb55c064867cf047dda097f92d51efad5b491dfb98f6bbb70cb36"
+checksum = "4e4246f76bdeff09eb48875a0fd3e2af6aada79d409d33011886d3e1581517d9"
 
 [[package]]
 name = "windows_x86_64_gnullvm"
-version = "0.42.2"
+version = "0.52.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "26d41b46a36d453748aedef1486d5c7a85db22e56aff34643984ea85514e94a3"
+checksum = "852298e482cd67c356ddd9570386e2862b5673c85bd5f88df9ab6802b334c596"
 
 [[package]]
 name = "windows_x86_64_msvc"
-version = "0.42.2"
+version = "0.52.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9aec5da331524158c6d1a4ac0ab1541149c0b9505fde06423b02f5ef0106b9f0"
+checksum = "bec47e5bfd1bff0eeaf6d8b485cc1074891a197ab4225d504cb7a1ab88b02bf0"
diff --git a/ext/tiktoken_ruby/Cargo.toml b/ext/tiktoken_ruby/Cargo.toml
index 2d1df26..9f5b07b 100644
--- a/ext/tiktoken_ruby/Cargo.toml
+++ b/ext/tiktoken_ruby/Cargo.toml
@@ -12,4 +12,4 @@ crate-type = ["cdylib"]
 [dependencies]
 magnus = { version = "0.6.1" }
 rb-sys = { version = "0.9.87", features = ["stable-api-compiled-fallback"] }
-tiktoken-rs = { git = "https://github.com/IAPark/tiktoken-rs.git" }
+tiktoken-rs = { version = "0.5.9" }
diff --git a/ext/tiktoken_ruby/src/lib.rs b/ext/tiktoken_ruby/src/lib.rs
index 068b4e6..32a5122 100644
--- a/ext/tiktoken_ruby/src/lib.rs
+++ b/ext/tiktoken_ruby/src/lib.rs
@@ -20,6 +20,11 @@ fn cl100k_base() -> CoreBPEWrapper {
     CoreBPEWrapper::new(core_bpe)
 }
 
+fn o200k_base() -> CoreBPEWrapper {
+    let core_bpe = tiktoken_rs::o200k_base().unwrap();
+    CoreBPEWrapper::new(core_bpe)
+}
+
 fn module() -> Result<RModule, magnus::Error> {
     define_module("Tiktoken")
 }
@@ -37,6 +42,7 @@ fn init() -> Result<(), Error> {
     factory_module.define_singleton_method("p50k_base", function!(p50k_base, 0))?;
     factory_module.define_singleton_method("p50k_edit", function!(p50k_edit, 0))?;
     factory_module.define_singleton_method("cl100k_base", function!(cl100k_base, 0))?;
+    factory_module.define_singleton_method("o200k_base", function!(o200k_base, 0))?;
 
     let ext_module = module.define_module("Ext")?;
     let bpe_class = ext_module.define_class("CoreBPE", class::object())?;
diff --git a/lib/tiktoken_ruby.rb b/lib/tiktoken_ruby.rb
index 57e2448..1d92879 100644
--- a/lib/tiktoken_ruby.rb
+++ b/lib/tiktoken_ruby.rb
@@ -64,13 +64,15 @@ def list_model_names
       :r50k_base,
       :p50k_base,
       :p50k_edit,
-      :cl100k_base
+      :cl100k_base,
+      :o200k_base
     ]
 
     # taken from the python library here https://github.com/openai/tiktoken/blob/main/tiktoken/model.py
     # that is also MIT licensed but by OpenAI
     MODEL_TO_ENCODING_NAME = {
       # chat
+      "gpt-4o": "o200k_base",
       "gpt-4": "cl100k_base",
       "gpt-3.5-turbo": "cl100k_base",
       "gpt-35-turbo": "cl100k_base",  # Azure deployment name
@@ -120,6 +122,7 @@ def list_model_names
 
     MODEL_PREFIX_TO_ENCODING = {
       # chat
+      "gpt-4o-": "o200k_base",  # e.g., gpt-4o-2024-05-13, etc.
       "gpt-4-": "cl100k_base",  # e.g., gpt-4-0314, etc., plus gpt-4-32k
       "gpt-3.5-turbo-": "cl100k_base",  # e.g, gpt-3.5-turbo-0301, -0401, etc.
       "gpt-35-turbo-": "cl100k_base",  # Azure deployment name