Did Einstein ever claim that light is a particle ?

No. He did not call it a photon either.

As Gemini AI explains:

In his 1905 paper on the photoelectric effect, Albert Einstein did not use the word "particle" to define light. Instead, he introduced the concept of light quanta (Lichtquanten in German). 

While he famously proposed that light behaves as if it consists of discrete, localized packets of energy, there are important nuances to how he expressed this:

1. Choice of Terminology

Einstein avoided the term "particle" because he was careful not to claim that light was a literal particle in the classical sense, which would have directly contradicted well-established wave theories. The term photon was not coined until 1926 by Gilbert N. Lewis, over two decades after Einstein's initial paper. 

2. "Heuristic" Point of View

Einstein titled his paper "On a Heuristic Viewpoint Concerning the Production and Transformation of Light". By calling it "heuristic," he was suggesting that treating light as discrete bundles was a useful mental or mathematical model to explain certain phenomena (like the photoelectric effect) that the wave theory could not. 

3. Wave-Particle Duality

Einstein was the first to suggest that light had a dual nature. He did not believe light was only a particle; rather, he argued that in certain interactions—specifically during emission and absorption—light behaves as if its energy is concentrated in finite chunks rather than spread smoothly through space like a classical wave. 

4. His Own Reflections

Even late in life, Einstein remained humble about the discovery, famously writing in 1951: "All these fifty years of conscious brooding have brought me no closer to the answer to the question, 'What are light quanta?'". 

In summary, while Einstein provided the first scientific proof for what we now call the particle nature of light, he strictly referred to them as energy quanta or light quanta.