threshold_ms = intercept_ms + per_token_ms * input_tokens. Lets the TTFT target scale with prefill work, e.g. "4s + L_in/8k" => intercept_ms=4000, per_token_ms=0.125 (4s base, +1s per 8k input tokens). slo + spec + test. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>