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perf(caching): selective copy instead of deepcopy entire history #57046

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perf(caching): selective copy instead of deepcopy entire history #57046

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10 changes: 6 additions & 4 deletions agent/prompt_caching.py
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Original file line number Diff line number Diff line change
Expand Up @@ -57,23 +57,25 @@ def apply_anthropic_cache_control(
messages, all at the same TTL.

Returns:
Deep copy of messages with cache_control breakpoints injected.
Shallow copy of message list with selective deep copies of modified messages.
"""
messages = copy.deepcopy(api_messages)
if not messages:
return messages
if not api_messages:
return api_messages

messages = list(api_messages)
marker = _build_marker(cache_ttl)

breakpoints_used = 0

if messages[0].get("role") == "system":
messages[0] = copy.deepcopy(messages[0])
_apply_cache_marker(messages[0], marker, native_anthropic=native_anthropic)
breakpoints_used += 1

remaining = 4 - breakpoints_used
non_sys = [i for i in range(len(messages)) if messages[i].get("role") != "system"]

@teknium1 teknium1 Jul 15, 2026

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Current main filters candidates through _can_carry_marker(..., native_anthropic=...) so empty/non-carrier OpenRouter turns do not spend breakpoint capacity. Preserve that filter when salvaging this selective-copy change; see current agent/prompt_caching.py:110-115 and tests/agent/test_prompt_caching.py:198-224.

for idx in non_sys[-remaining:]:
messages[idx] = copy.deepcopy(messages[idx])
_apply_cache_marker(messages[idx], marker, native_anthropic=native_anthropic)

return messages