eth_fillTransaction (unsupported by Alchemy)

[tuler]

I'm using baseSepolia chain with Alchemy and it looks like viem is calling eth_fillTransaction on simulateContract + writeContract, which is an unsupported method on Alchemy. Somehow it's not being flagged as unsupported in viem, and I keep getting errors in my Alchemy request logs.

[sueun-dev]

Thanks for reporting this with provider context.

eth_fillTransaction is not a widely supported RPC method across providers, so if viem reaches that path against Alchemy on baseSepolia, the failure is expected on the provider side. A practical workaround is to provide all tx fields up front (nonce, gas, fee fields, etc.) so there is no fill step needed before send/sign.

It would also help to post a minimal repro (client setup + one simulateContract/writeContract call). That should make it easier for maintainers to confirm whether this is expected behavior, a capability-detection gap, or a bug in method selection.

[tuler]

Opened an issue for it #4381