Is the C4 model still worth using?
Yes, as a way of thinking about levels of detail: separating context, containers and components stops the single unreadable everything-diagram. It is a notation, not a mechanism, so it does not solve staleness on its own; pair it with something that checks the diagram against the code.
From Architecture diagrams that stay true, published 9 August 2026. That article is where the reasoning behind this answer is set out, including what it does not cover.