MiniMax-M3 ships server-side automatic prefix caching on the
Anthropic-compatible endpoint (content-keyed, no marker needed —
see platform.minimax.io/docs/api-reference/text-prompt-caching).
cache_control markers are NOT on its explicit-cache support list
(which covers only M2.7/M2.5/M2.1/M2).
Emitting markers on M3:
- wasted serialization overhead
- risked perturbing the server-side prefix hash
- gave users a false sense of explicit-cache savings (the
cache_read_input_tokens field carries a +128 constant floor
and cache_creation_input_tokens is always 0 for M3)
Also add an opt-in debug=True parameter to normalize_usage() that
emits a debug-level log line carrying the observable cache fields.
This is the only reliable cache signal for M3 — off by default,
debug-level, scoped to the anthropic_messages wire, so production
callers see no impact.
Pin both changes with 8 new tests:
- 4 M3 tests covering provider, host, and custom-provider paths
- 1 regression guard ensuring M2.x caching is unaffected
- 3 observability tests (off-by-default, on-with-M3, on-with-Claude)
Verified end-to-end against api.minimaxi.com/anthropic/v1/messages
with MiniMax-M3[1m]: identical system prompt hit-rate with and
without markers; cache_read field is unreliable (128 floor),
input_tokens drop (8467 -> 1) is the real hit signal.
Hermes Agent
c1e2529ae2