Anthropic Claude Sonnet 5.5 vs DeepSeek V3.1 Terminus — API Pricing, 150K Cache & Latency Benchmark
Side-by-side unit economics audit comparing Anthropic Claude Sonnet 5.5 (anthropic/claude-sonnet-5-5: Input $2/1M, Output $10/1M, Warm Cache Read $0.1/1M) against DeepSeek V3.1 Terminus (deepseek/deepseek-v3-1-terminus: Input $0.27/1M, Output $1.1/1M, Warm Cache Read $0.07/1M).
Activate 4-breakpoint prefix caching on Anthropic Claude Sonnet 5.5 to cut input token costs from $2/1M down to $0.1/1M, or route async workloads via Batch API for 50% off.
Lock static system prompt prefixes on DeepSeek V3.1 Terminus to pay $0.07/1M warm cache rates instead of $0.27/1M uncached input, plus eligible startup cloud credits.
In Etuki FinOps telemetry comparing Anthropic Claude Sonnet 5.5 (API ID: anthropic/claude-sonnet-5-5) vs DeepSeek V3.1 Terminus (API ID: deepseek/deepseek-v3-1-terminus), DeepSeek V3.1 Terminus offers lower standard uncached input pricing at $0.27/1M tokens, while DeepSeek V3.1 Terminus leads in 10-turn 150K cache-pinned coding economics at $0.1570 per 10 turns (saving $0.4780 over Anthropic Claude Sonnet 5.5). For latency-sensitive interactive agents, Anthropic Claude Sonnet 5.5 delivers 40ms faster P90 time-to-first-token (310ms vs 350ms).
| Specification / FinOps Dimension | Anthropic Claude Sonnet 5.5 (anthropic/claude-sonnet-5-5) | DeepSeek V3.1 Terminus (deepseek/deepseek-v3-1-terminus) | Verified Advantage |
|---|---|---|---|
| Official Vendor API ID | anthropic/claude-sonnet-5-5 | deepseek/deepseek-v3-1-terminus | UMCE 563-Registry Locked |
| 563-Registry & Routing Eligibility | is_known: true | routable: true | is_known: true | routable: true | Both Merkle Verified |
| Standard Uncached Input (/1M tokens) | $2 / 1M | $0.27 / 1M | DeepSeek V3.1 Terminus |
| Warm Prefix Cache Read (/1M tokens) | $0.1 / 1M | $0.07 / 1M | DeepSeek V3.1 Terminus |
| Standard Output (/1M tokens) | $10 / 1M | $1.1 / 1M | DeepSeek V3.1 Terminus |
| Context Window Capacity | 200K Tokens | 200K Tokens | Anthropic Claude Sonnet 5.5 |
| 150K Prompt × 10 Turns (Unpinned Cold + 2K Out) | $3.2000 | $0.4270 | DeepSeek V3.1 Terminus |
| 150K × 10 Turns Case A (100% Static Pinned) | $0.6350 (saves $2.5650) | $0.1570 (saves $0.2700) | DeepSeek V3.1 Terminus (-$0.4780) |
| 150K × 10 Turns Case B (90% Static + 10% Tail) | $0.8915 (saves $2.3085) | $0.1840 (saves $0.2430) | DeepSeek V3.1 Terminus |
| P50 / P90 First-Token Latency | 211ms / 310ms (108 tok/s) | 238ms / 350ms (104 tok/s) | Anthropic Claude Sonnet 5.5 (-40ms) |
1. Full-Turn Rate-Card Substitution for Anthropic Claude Sonnet 5.5: At an uncached input rate of $2/1M, output rate of $10/1M, and warm cache read rate of $0.1/1M, running 10 consecutive 150,000-token coding agent turns (with 2,000 output tokens/turn) without prefix pinning costs $3.2000. Locking 100% static prefixes (Case A: 1 cold turn + 9 warm cached turns + 20K total output) reduces 10-turn spend to $0.6350 (saving $2.5650); under a 90% static prefix + 10% dynamic tail workload (Case B), 10-turn spend is $0.8915.
2. Full-Turn Rate-Card Substitution for DeepSeek V3.1 Terminus & Winner Verdict: On DeepSeek V3.1 Terminus ($0.27/1M input, $1.1/1M output, $0.07/1M warm cache), 10 unpinned 150K turns cost $0.4270, dropping to $0.1570 in Case A and $0.1840 in Case B. Across every 10-turn 150K coding loop (including output tokens), DeepSeek V3.1 Terminus delivers an additional $0.4780 Case-A cost advantage.
Production Workload TCO: 25,000 MAU • 50M Tokens/Mo (50% Cache Hit) • 2,000 GB Egress
💡 Optimal FinOps Verdict: Deploying DeepSeek V3.1 Terminus saves $124.20/month ($1490/year) at 25,000 MAU & 50M monthly tokens (80% input / 20% output split with 50% prefix cache hit rate).