Suspected Gemini 4 Pro Spotted in Anonymous Arena Testing
Between 09-26 and 09-27, multiple users reported spotting an unreleased checkpoint suspected to be Google Gemini 4 Pro on LMArena, possibly tested anonymously under the placeholder name "gemini-3.8-flash." Leaks claim it outperforms Claude Opus 5.5 and GPT-6 Astra at roughly 1/5 the cost with 2M context. None of this is officially confirmed, but it has triggered intensive community blind testing.
Confirmed
- On 09-26, @cedricchee found Google had deployed a new Gemini 4 Pro checkpoint on Arena competing against GPT-6 Astra and Fable, with Gemini 4 Pro currently leading; @markk posted "don't underestimate Google DeepMind," previewing a strong comeback (unverified).
- The same day, WorldofAI summarized the week's leaks: the Barium-B checkpoint reportedly beat Claude Opus 5.5 and GPT-6 Astra on new benchmarks, with release timing predictions; the roundup also mentioned Kimi K4 and a mystery model.
- On 09-27, @CodeByPoonam relayed @TimJayas's testing: a model routed under "gemini-3.8-flash" on LMArena performed like the rumored Gemini 4 Pro — a mechanical hummingbird prompt produced high-quality output close to Fable, clearly better than current flagships.
- @CodeByPoonam also compiled 10 community generation examples; @Wanderspor relayed a Reddit roundup claiming leaked specs of 1/5 competitor cost and 2M context, which would upend frontier-model economics if released in October.
Unconfirmed
- Whether the anonymous model is truly Gemini 4 Pro: @aiforsuccess's comparison screenshots (relayed by @CodeByPoonam) showed it "completely crushing" Opus 5.5, but the poster cautioned it cannot be 100% confirmed; @markk's claims are also unverified.
- A same-prompt comparison against Claude Opus 5.5 High concluded Gemini 4 "has not yet reached" that level, contradicting the "crushing" narrative.
- No official data exists on rankings, pricing, or release timing.
Why it matters
- If true, Google would field a highly competitive next-gen flagship against OpenAI (GPT-6 Astra) and Anthropic (Opus 5.5), potentially reshaping frontier-model economics with drastically lower costs — driving intense community attention, with some calling it potentially the biggest comeback in AI history.
2026-09-26 ~ 2026-09-27 · 8 related posts
- Episode 1: Suspected Gemini 4 Pro Spotted in Anonymous Arena Testing(2026-09-26, 8 posts)
- Episode 2: Google's Gemini 4 Enters Final Training Push, May Launch by Year-End(2026-09-26, 2 posts)
- Episode 3: Leaked Gemini 4 Pro Benchmark Sparks Buzz Ahead of OpenAI DevDay(2026-09-28, 4 posts)
- Episode 4: Gemini 4.0 Pro and Multiple New Models Tipped for Release Within Weeks(2026-10-01, 2 posts)
- Episode 5: Google Unveils Gemini 4 Argon with 1M-Token Output, Defense-First Rollout(2026-10-01, 118 posts)
- Episode 6: Gemini 4 Leaks Flood Out as Bloomberg Reports Internal Struggles(2026-10-01, 35 posts)
- Episode 7: Gemini 4 Argon Shines in Long-Horizon Coding Benchmarks(2026-10-01, 2 posts)
- Episode 8: Viral "Gemini 4 Argon" blog page turns out to be a hoax(2026-10-01, 6 posts)
- Episode 9: Google's Gemini 4 Argon agents free over 300 TiB of datacenter memory(2026-10-01, 3 posts)
- Episode 10: Reported Gemini 4 Argon Beats Quantum Algorithm Baseline by 40% in Minutes(2026-10-01, 2 posts)
- Episode 11: Google Engineer Praises Gemini 4 Argon's Troubleshooting Skills(2026-10-01, 3 posts)
- Episode 12: Polymarket Bets Surge on Google as Gemini 4 Rumors Swirl(2026-10-01, 2 posts)
- Episode 13: Gemini 4 Expectations Split as Google Restart Pretraining(2026-10-01, 2 posts)
- Episode 14: Blogger Defends Google's TPU Edge as Gemini 4 Hype Builds(2026-10-02, 2 posts)
- Episode 15: Rumors Claim Google Has Far Stronger Internal Models(2026-10-02, 2 posts)
- Episode 16: Reported Google Gemini 4 Argon supports 1M-token outputs(2026-10-02, 2 posts)
- Episode 17: Gemini 4 Praised as Astra-Class at One-Fifth the Price(2026-10-03, 3 posts)
- Episode 18: Gemini 4 Argon Tops Multiple Leaderboards, Sparking Debate(2026-10-04, 3 posts)
- Episode 19: Gemini 4 Argon Surfaces in Docs and Cloud Quotas Ahead of Launch(2026-10-04, 3 posts)
Primary sources
- [source] New Gemini 4 Pro checkpoint spotted in Arena, outranking GPT-6 Astra — cedric_chee · 2026-09-26
- Gemini 4 Pro Spotted in AI Arena: Leak Claims Google's Comeback Is Coming — mark_k · 2026-09-26
- Gemini 4 Pro Leak Allegedly Beats Opus 5.5; Kimi K4 and Stealth Model Spotted — WorldofAI · 2026-09-26
- Rumored Gemini 4 Pro Checkpoint Wows Arena Testers: 10 Wild Examples — CodeByPoonam · 2026-09-27
- Rumored Gemini 4 Pro Checkpoint Reportedly Outshines Opus 5.5 on Arena — CodeByPoonam · 2026-09-27
- [source] Arena Reportedly Testing Gemini 4 Pro Under gemini-3.8-flash Codename — CodeByPoonam · 2026-09-27
- Gemini 4 Pro checkpoint spotted in Arena as "gemini-3.8-flash", closing on Opus — CodeByPoonam · 2026-09-27
- [source] Leaked Gemini 4 Pro specs: 2M context at ~1/5 rival pricing would reset frontier economics — Wanderspor · 2026-09-27