litellm/litellm-rust/crates/token-counter/README.md
devin-ai-integration[bot] 0abd9267c1
feat(tokenizer): preserve Python defaults with opt-in Rust dispatch (#42174)
* ci: benchmark and gate an installed release wheel

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* ci: simplify installed-wheel benchmark check

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* feat(rust): add native tokenizer codec

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* refactor(tokenizer): route Python tokenization through the Rust extension

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* style(lint): format tokenizer call

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* fix(packaging): restore runtime dependencies and native images

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* fix(tokenizer): preserve Python SDK behavior with Rust tokenizers

* fix(tokenizer): restore compatibility paths

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* refactor(tokenizer): count custom tokenizers directly

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* fix(tokenizer): preserve caller-supplied Python tokenizer counts

* fix(tokenizer): reuse packaged vocabularies in the native wheel

* refactor(rust_bridge): route token counting through the catalog as RUST_OPT_IN

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* fix(spend_tracking): compare tokenizer groups by value

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* chore(deps): re-resolve filelock under the <4.0 pin

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* fix(llms): align transformation override signatures with base configs

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* build(rust): use fat LTO to keep the native wheel under the 35 MB limit

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* feat(tokenizer): preserve Python defaults with opt-in Rust dispatch

* test(proxy): tolerate missing litellm.utils.Tokenizer when patching it

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* test(proxy): patch the tokenizer dispatch function instead of the removed alias

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* feat(tokenizer): give the Rust wrappers the tiktoken and tokenizers surface

Callers of litellm.encoding and litellm.create_tokenizer must see the same
read-only API whichever backend the catalog selects.

- OpenAIEncoding mirrors tiktoken.Encoding: n_vocab, max_token_value,
  token_byte_values, encode_single_token, encode_with_unstable,
  encode_to_numpy, decode_with_offsets, is_special_token, repr; the Rust
  tiktoken crate keeps a Vocabulary beside each CoreBPE and reports the
  requested encoding name (gpt2 stays gpt2).
- HuggingFaceTokenizer mirrors the read-only tokenizers.Tokenizer surface
  (token_to_id, id_to_token, get_vocab, get_vocab_size,
  get_added_tokens_decoder, num_special_tokens_to_add, padding, truncation,
  encode_special_tokens, from_buffer); HuggingFaceEncoding gains the
  char/word/token lookups, pad, truncate, set_sequence_id and merge.
  Mutators stay on the Python tokenizer.
- from_json/from_pretrained claim the fork gate only when the huggingface
  feature is compiled in; the surrogate fallback matches on the Codec.
- Tokenizer caching is keyed on the same catalog Context the dispatch runs
  on; rust_tokenizer reads the encoding name without loading an encoding;
  LITELLM_RUST parsing is cached.
- Drop the unused tiktoken_encoding_for_model export and Error::Download.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* fix(tokenizer): close the exhaustive matches with assert_never

CodeQL reads a `match` over a Literal with no default arm as an implicit
`None` return. `assert_never` makes the exhaustiveness explicit for both the
HuggingFace tokenizer loader and the Rust token-counter factory.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* feat(tokenizer): derive the fast counter from the shared tokenizer

The count-only counter (`fast` feature) and the codec each parsed the same
artifact: TokenCounter took the Anthropic JSON and the tiktoken rank files
from Python while Tokenizer loaded them again. One parse now serves both.

- FastTokenizer builds from a model another loader holds: `from_shared`
  takes the Arc<tokenizers::Tokenizer> the HF codec keeps, and
  `from_*_pairs` take the ranks the tiktoken vocabulary already parsed.
- `FastCounter::fast_counter` in the core crate derives it from either codec;
  encodings the fast scanner does not reproduce are refused.
- Native `Tokenizer.count(text, fast=False)` opts into that counter, built
  once per tokenizer on first use; `TokenCounter.from_tokenizer(tokenizer,
  fast=False)` replaces the JSON and rank-file constructors.
- The Python route counts over the native tokenizers the codec path shares
  (`native_encoding`, `native_anthropic`) and no longer reads rank files;
  the packaged Anthropic tokenizer has one loader, `tokenizer_dispatch.anthropic`.
- Public wrappers gain `count(text, fast=False)`.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

---------

Co-authored-by: Yujong Lee <yujong@berri.ai>
Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
2026-09-22 04:41:11 +00:00

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# Token counting
`Tokenizer` is the text-counting interface. `TextCodec` adds encoding, decoding, and a name. `TokenCounter` applies LiteLLM request, message, and tool accounting using any `Tokenizer`
Counts follow the codec: tiktoken treats special-token spellings as ordinary text, while Hugging Face applies its added tokens, post-processing, padding, and truncation. `fast=True` preserves those semantics and requests acceleration where available. Unsupported configurations use the normal codec, including tiktoken encodings without a scanner and builds without the `fast` feature. Invalid input and process-guard errors still propagate. Runtime request counting currently uses the normal codec; the custom accelerator is retained for explicit use and testing
`FastCounter: TextCodec` exposes an optional accelerator over a loaded codec. `None` means callers should use that codec. The Python bridge caches this selection per immutable tokenizer, shares it with request counters, and initializes it with the GIL released. Hugging Face can also choose the full encoder per input when added tokens require it
The `fast` feature provides `fast::FastTokenizer` from `litellm-token-counter-fast`. `TokenCounter::from_json_fast` uses this implementation
The `huggingface` feature provides `huggingface::HuggingFaceTokenizer` through the upstream `tokenizers` library. `TokenCounter::from_json` uses this implementation
The `tiktoken` feature provides `tiktoken::TiktokenTokenizer` through `tiktoken-rs`. Select an encoding with `TokenCounter::from_tiktoken`. The supported names are `cl100k_base`, `o200k_base`, `o200k_harmony`, `p50k_base`, `p50k_edit`, `r50k_base`, and `gpt2`
All three backends are enabled by default in this crate and the Python extension. With `default-features = false`, Rust callers can supply their own `Tokenizer` to `TokenCounter::new` without compiling a built-in backend
Python `tiktoken` and `tokenizers` remain runtime dependencies and the default implementations. The catalog independently selects the tokenizer and request-counting routes. Enabling Rust changes factory dispatch; existing tokenizer objects keep their backend. Native Hugging Face wrappers provide an immutable encoding and decoding API, while training and mutable configuration remain available through the Python backend
Budget checks, cost calculation, and the `max_tokens` adjustment policy belong to `litellm-core-utils`. The counter does not own prices, budgets, or request limits
Run the feature matrix with:
```sh
cargo test -p litellm-token-counter
cargo test -p litellm-token-counter --no-default-features
cargo test -p litellm-token-counter --no-default-features --features fast
cargo test -p litellm-token-counter --no-default-features --features huggingface
cargo test -p litellm-token-counter --no-default-features --features tiktoken
```