[Frontend] Add cache_salt support to Anthropic Messages API - #49498
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DarkLight1337 merged 4 commits intoAug 1, 2026
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The OpenAI-compatible Chat/Completions APIs accept a `cache_salt` for explicit prefix-cache isolation in multi-user deployments, but the Anthropic Messages API did not expose it, forcing clients on the Anthropic schema to switch API formats to use it. Add `cache_salt` to `AnthropicMessagesRequest` and thread it through `_build_base_request` into the internal `ChatCompletionRequest` (which already owns the field and its `check_cache_salt_support` validator), mirroring the existing `kv_transfer_params` pass-through. Behavior is unchanged when the field is omitted. Fixes vllm-project#46688 Signed-off-by: aeon-x <talexcao@gmail.com>
aeon-x
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AndreasKaratzas,
DarkLight1337,
NickLucche,
aarnphm,
mgoin and
robertgshaw2-redhat
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July 23, 2026 00:57
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Hey @DarkLight1337 @robertgshaw2-redhat @aarnphm @NickLucche @AndreasKaratzas @mgoin Can help take a look at this PR? Thanks a lot. |
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PR looks alright, but since I dont see any comments on the RFC, I will wait for @DarkLight1337 to give the go/no-go. |
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Thanks a lot for your review! |
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Purpose
Closes #46688.
The OpenAI-compatible Chat Completions / Completions APIs accept a
cache_saltfor explicit prefix-cache isolation in multi-user deployments. The Anthropic
Messages API (
/v1/messages) did not expose it, so clients built on theAnthropic schema had to switch API formats just to get deterministic
prefix-cache isolation.
Change
cache_salt: str | NonetoAnthropicMessagesRequest, with the samedescription as the OpenAI chat field.
_build_base_requestinto the internalChatCompletionRequest, which already owns the field and itscheck_cache_salt_supportvalidator — so validation and engine behaviormatch the OpenAI routes exactly.
Only the Messages (generation) path is affected;
AnthropicCountTokensRequestis untouched (no generation, no prefix-cache isolation concern). Behavior is
unchanged when
cache_saltis omitted (defaults toNone).Test
tests/entrypoints/anthropic/test_anthropic_messages_conversion.py::TestCacheSalt:cache_salton the Anthropic request reaches the convertedChatCompletionRequest.None(unchanged default).Note: I was unable to run the suite locally (no CUDA/torch on my dev machine);
the files pass
py_compileand the change mirrors the existingkv_transfer_paramspass-through — relying on CI to execute the tests.