What the law currently says is that "coffee shops" are only allowed to sell cannabis to people residing in the Netherlands (ingezetenencriterium) and can check that by asking a proof of registration from a Dutch municipality (together with a valid ID). This rule has replaced the "weed pass" concept, which has been abandoned, and is in principle valid nationwide.
However, it's up to the municipalities to integrate this new rule in their local "coffee shop policy" and coordinate with the police and the public prosecutor to enforce it. As of mid-2015, most municipalities in the Netherlands did so and municipalities in the south (which drove the reform in the first place) seem especially aggressive in enforcing it (I saw media reports about police raids and coffee shop closures).
But Amsterdam most certainly did not, and various press reports suggest that it first agreed to close coffee shops that were too close to schools intead of implementing the new rule and then decided to postpone that while waiting for a court decision. The justice minister also went on record (in 2012, as the new rules were introduced) stating that the ministry would not try to enforce the residency rule in Amsterdam on its own and could not specify when it would be implemented.
As a practical matter, in Amsterdam, as of Spring 2016, you can buy whatever you want and smoke on the premises without any problem, no questions asked. Personally, I do not smoke and obviously cannot vouch that each and every shop will serve you but that's what I have observed and I can't imagine shops would restrict purchases unless the municipality forces them to. You can also buy weed as a tourist in The Hague (and, I think, Rotterdam and Utrecht) but they tend to be stricter with regards to other products like space cakes.