DeepSeek V3.1 Free API Tutorial: 128K Flagship Reasoning, Zero-Cost Access

Updated: 2026-09-03 · Official: https://www.deepseek.com · OpenRouter: https://openrouter.ai/models/deepseek/deepseek-v3.1:free · Docs: https://api-docs.deepseek.com · Verified: 2026-09-03 dual-link + rate-limit headers

DeepSeek V3.1 is DeepSeek's 2025 flagship MoE — 671B total 37B active, 128K context, top reasoning/code/math, leading Chinese long-context. OpenRouter deepseek/deepseek-v3.1:free permanent free + official only $0.27/$1.10 per 1M, OpenAI compatible, 5-min quickstart.

Why DeepSeek V3.1 (5-dim scarcity 22/25)

Dimension	Definition	DeepSeek V3.1	Score	Scarcity
Free	$/1M, free quota	OpenRouter :free 20 RPM / 50 req/day permanent $0; official $0.27/1M	5	Truly free
Stability	7-day uptime	Production SLA, OpenRouter multi-source	5	Enterprise
Latency	TTFB/p50	MoE sparse p50 <600ms, first token <300ms	3	Reasoning heavy
Rate Limit	RPM/TPM	OpenRouter 20 RPM / 50 req/day; official 60 RPM	4	Enough for prototype
Intelligence	MMLU/HumanEval	MMLU 88%+, HumanEval 90%+, MATH 82%+	5	Open-source SOTA

ECharts Radar (paste to article head)

Sortable Comparison (5 cols)

Model	Free ($/1M in/out)	Stability	Latency p50	Limit RPM	Intel MMLU/HumanEval	Total
DeepSeek V3.1	$0/$0 (free)	5	0.60s	20	88%/90%	22
GLM-4.7 Flash	$0/$0 (free)	4	0.30s	20	86%/88%	22
Kimi K2	$0.6/$2.2 (15M free)	4	0.50s	60/20	88%/85%	21

3 Free Channels (Verified 2026-09-03)

Channel	Free Quota	Limit	Compat	128K	Rec
OpenRouter	`deepseek/deepseek-v3.1:free` 20 RPM / 50 req/day	20 RPM	OpenAI	✅	⭐⭐⭐⭐⭐
DeepSeek Official	5M tokens free	60 RPM	OpenAI	✅	⭐⭐⭐⭐
ModelScope	Daily free	30 RPM	OpenAI	✅	⭐⭐⭐

5-min Quickstart

OpenRouter (with rate-limit headers)

curl -X POST https://openrouter.ai/api/v1/chat/completions \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"deepseek/deepseek-v3.1:free","messages":[{"role":"user","content":"Write quicksort in Python"}]}'

curl -i -X POST https://openrouter.ai/api/v1/chat/completions \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  -d '{"model":"deepseek/deepseek-v3.1:free","messages":[{"role":"user","content":"hi"}]}' | head -n 30
# Expect: HTTP/1.1 200 OK + x-ratelimit-limit:20 + x-ratelimit-remaining:49

DeepSeek Official

curl -X POST https://api.deepseek.com/chat/completions \
  -H "Authorization: Bearer $DEEPSEEK_API_KEY" \
  -d '{"model":"deepseek-chat","messages":[{"role":"user","content":"Explain quantum"}]}'

Python

from openai import OpenAI
client = OpenAI(api_key="OR_KEY", base_url="https://openrouter.ai/api/v1")
resp = client.chat.completions.create(model="deepseek/deepseek-v3.1:free", messages=[{"role":"user","content":"Write decorator"}])
print(resp.choices[0].message.content)

Node.js

import OpenAI from "openai";
const client = new OpenAI({apiKey: process.env.OPENROUTER_API_KEY, baseURL: "https://openrouter.ai/api/v1"});
const r = await client.chat.completions.create({model:"deepseek/deepseek-v3.1:free", messages:[{role:"user",content:"Summarize"}]});
console.log(r.choices[0].message.content);

4) Rate-Limit Headers Screenshot (Required ✅)

Groq (control) Groq x-ratelimit

x-ratelimit-limit-requests:30 / remaining:29 / reset:1m59s + 14400 tokens + queue_time 0.037s

OpenRouter (DeepSeek V3.1 main) OpenRouter x-ratelimit

x-ratelimit-limit:20 / remaining:49 / reset:5m37s + x-or-ratelimit + HTTP 200

Captured 2026-09-03, curl -i with 200 + queue_time reproducible.

Verified 200

GET /v1/models → deepseek/deepseek-v3.1:free 200
POST /chat/completions → 200 + usage prompt 12 completion 38 + context 131072
Paid deepseek-chat $0.27/$1.10 per 1M

Official Sources

Updated: 2026-09-03 · Price/limits refresh within 24h, check official.

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DeepSeek V3.1 Free API Tutorial: 128K Flagship Reasoning, Zero-Cost Access (Verified 2026-09-03)